Closed-loop extraction

A closed-circuit extraction system is a term used to describe equipment that enables processors to extract active compounds from the cannabis plant using a variety of solvents in a safe and efficient environment.

A closed-loop system means that the solvent used to extract the compounds from the plant material does not come into contact with the outside environment at any point during the extraction process.

What's more, the solvent completes a complete loop during its phase change, from liquid to gas and back to liquid - the solvent starts and ends in the same space.

How does a closed-loop system work?

Closed-loop systems vary mechanically, depending on the solvent to be used. However, the general method remains the same. There are three main containment zones: a container for the primary solvent, one for the cannabis plant material and another for the extract obtained.

Depending on the type of solvent used, for example for butane extraction or a carbon dioxide (CO2) extraction, In order to extract all the valuable compounds, such as cannabinoids and terpenes, it may be necessary to pass the solvent through the cannabis plant material several times. Butane, for example, is one of the most efficient solvents, capable of extracting almost all the essential properties in a single pass through the system. By contrast CO2 is a much more selective solvent, and it will take several passes, and several hours, to fully capture all the intoxicating and therapeutic properties of the cannabis plant.

The process begins with a tank of liquid solvent or gas that is mechanically converted into liquid solvent. The next step is to let the liquid solvent flow into the tank with the cannabis buds or waste. At this stage, the solvent will dissolve the plant's active compounds and create a solution. The final tank is where the resulting extract goes, and where the initial solvent used is evaporated from the solution using heat. As the solvent evaporates into a gas, this rises and is condensed in the first tank. The solvent can then be reused, either on the same cannabis or for a new batch.

What are the risks?

Each solvent presents its own risks, and precautions are taken according to the solvent used. Some solvents are flammable, others asphyxiating. Some operate at low pressure, others at high. Each solvent is different and requires different technical controls to ensure that all risks are mitigated during the extraction process.

Although it has acquired a bad reputation in the media due to the explosions that have occurred during 'open-air extraction» - where the solvent is exposed to air during the extraction process - butane is classified as »generally considered safe«. Its flammability, however, makes the use of a closed-circuit system the only available method for butane extraction, as open-air extraction has proved to be a dangerous alternative.

CO2, although non-flammable, is an asphyxiant that requires extremely high pressure to transform it from a gas into a supercritical fluid capable of extracting cannabis compounds. The technical controls used in these systems monitor the relative concentration of CO2 in the air to ensure worker safety throughout the process. Safety measures are taken, whatever the solvent, and sensors are in place to detect any trace of gas.